1. Field of the Invention
The present invention relates to an image forming apparatus implemented by a distributed control system including a plurality of CPU groups having a hierarchical structure.
2. Description of the Related Art
Centralized control using one CPU is performed for printer device control of an image forming apparatus using an electrophotographic system. An increase in CPU load due to centralized control requires a higher performance CPU. In addition, as the control load of the printer device rises, communication cables (a bundle of communication lines) need to be laid from a CPU board to distant load driver units and many long communication cables are needed. To solve these problems, a control form is receiving a great deal of attention, in which control modules which build an electrophotographic system are assigned to sub-CPUs (see Japanese Patent Laid-Open No. 2006-256275).
To apply a system configuration to perform distributed control to an image forming apparatus, and decrease the number of development processes and the cost, it is effective to adopt the same CPU circuit board arrangement, and control CPU circuit boards and loads in accordance with loads connected to the CPU circuit boards. Such CPU circuit boards can be developed to a plurality of products by increasing/decreasing the number of CPU circuit boards used. In this way, demand has arisen for development into a plurality of products having different product specifications while decreasing the number of development processes and the cost. In a system in which a plurality of CPUs perform distributed control, it is indispensable to decrease the number of components on the CPU circuit board and reduce the cost. The cost can be reduced using, for example, a clock oscillator incorporated in each CPU.
However, clock oscillators incorporated in CPUs have poor accuracy and a large individual difference. Even when external clock oscillators are used, medium- and long-term errors occur owing to their individual differences. When a plurality of CPUs individually control actuators such as stepping motors, the errors of the built-in clock oscillators or external clock oscillators lead to an error in speed between the stepping motors which control paper conveyance, pulling or flexing paper. Even when a predetermined time is measured, the time measurement results of the respective CPUs differ from each other, generating a paper jam, color misregistration, or the like.